Optical instrument especially applicable to range-finders.



H. D. TAYLOR. OPTICAL INSTRUMENT 'ESPECIALLYIAPPLICABLE:TO RANGE FINDERS.

APPLICATION FILED OCT. 4 I913.

Pate-Med May 18,1915;

UNITED STATES FATE HAROLD DENNIS TAYLOR, 0F BISHOPHILL, ENGLAND, ASSIGNO R 0F ONE-HALF TO ARTHUR HUNGERFORD POLLEN, OF LONDON, ENGLAND.

OPTICAL INSTRUMENT ESPECIALLY APPLICABLETO RANGE-FINDERS.

Specification of Letters Patent.

Patented May 18, 1915.

Application flled October 4, 1913. Serial No.793,293.

To all whom it may concern.

Be it known that I, HAROLD DENNIS TAY- LOR, subject of the King of Great Britain,

. This invention relates to means for .inm creasing the brilliancy of the image 0bserved in certain classes of. optical instruments in which the emergent beam is not of a circular form. The best known instrument of-this type'is the rangefinder of the kind in which. a single telescope objective is employed, the upperhalf of which projects the lmage seen by one end of the instrument, and the lower half of which projects the image seen by theother end of the instrument into a common field of view.

The emergent beam in this case is not of a 0 n u a clrcular form, its dimensions are greater in a horizontal direction than in a vertical direction, and it is consequently ill-adapted to fill the circular pupil of the observers By means of this invention, I am enabled to modify the path of the rays through the instrument so that the emergent beam has approximately the same vertical and horizontal dimensions. This has the effect as will be seen hereafter of increasing the brightness of the image.

In order that the leading principle of the invention may be readily understood, I have, in the accompanying drawings, illustrated the various forms of the emergent beam.

In these drawings: Figure l is a diagrammatic view, showmgth'e upper and lower halves of the image superposed, one upon the other; Figs. 2 and-3 are similar views showing, in dotted 1'" es, the forms-of the beam relatively to the aperture of the observers eye; Fig. Mis also a diagrammatic view showing the result of interposingapparatus in the path of the beam to convert the forms of image appearing in Figs. 1 and Zinto a square image; Fig. 5 is also a diegraimnatlc view showing the relative posinQFFICE.

tions of the instrumentalities for producing 7 that result; Figs. 6 and 7 are views in ele- 1 yation and plan, respectively, of a separatmg prism, a separated pa1r of positive and negative achromatlo lenses,

prism, and a hand prismpand Figs. 8 and 9 are detail views.

It is Vwell known that the maximum brightness of an image obtainable with an optical instrument is that which is observed filled with light, that is, when the minimum cross section of the emergent beam is the with light and the brightness of the image will suffer, and any diminutionof the magwhen the pupil of the eye is ust completely i nification will result in an increased diame-- l ter of the emergent beain. Thefextra light so obtained cannot enter the pupil of the eye but falls outside of it and will therefore not enhance the brilliancyof the image in any way. p I

In short base rangefinders, of the type above referred to, the emergent beams from upper and lower imagesare of the shape shown in Fig. 1, and are in fact the images of thehalvs' of the object glass produced by the various lenses or the like traversed b the beam before it emerges from the eyepiece. Such images can be observed by interposing a ground glass screen in the emergent beams. Owing to the fact that the 7 image of the upper half of the objective-is superposed on that of the lower half as shown in Fig. 1 across section of the double emergent beam is obtained which has roughly the form of a parallelogram whose width is twice its height. It is clear? that this form of emergent beamiis ill-adapted to; fill the circular aperture ofthe observers eywhich is shown in dotted lines in"; Figs. 2 and 3'; Fig. 2 shows the case in which the magnification is so chosen as just'to fill the eye but leaving a large amount of wasted light on each side, and Fig. 3 shows the case in which almost the whole beam enters the eye but the pupil remains unfilled in its beam and yet only a small amount of light falls outside and is wasted. According to one method of carrying out the invention, I introduce a pair of more or less widely separated cylindrical lenses, one positive and one negative, whereby the horizontal magnifying power is doubled, or thereabout, while the vertical magnifying power remains the same. These lenses may be arranged in any suitable position between the object glass and the eye piece and produce an emergent beam whose cross section much morenearly corresponds in shape with. the circular aperture of the observers eye, so that if a suitable magnification is chosen, the eye can be filled and leave only a small amount of wasted light. A secondary effect produced by these lenses is that the image of the object observed, such as a ship, has its horizontal dimensions doubled relatively I to the vertical dimensions, the field of view having the form of a horizontal oval instead of being circular. While this distortion of the image may be objectionable in some cases, it isimmaterial in the case of a rangefinder, and the increased luminosity obtained is of the greatest possible importance, while the increasedhorizontal magnification that is thereby obtained without any sacrifice of light enables the observer to ob tain coincidence of the upper and lower images more exactly than he would otherwise do, and so the efiiciency of the rangefinder is increased. 7

I will now give a more exact description of one method of carrying out my invention;

In Figs. 6 and 7, there is to be seen a halving or separating prism H on whose first surfaces are thrown the superimposed imagesof distant objects formed by the objective situated somewhere to the left.

These images are views of the distant object as seen by the upper half of the objective through the left hand window and the lower half of the objective through the right hand window of the rangefinder. Cemented to the halving prism Ti is an achromatic lens, whose function it is to throw separated-out images of the object glass onto the first of the left reflecting prism 1 which reflects one moiety of light into the left erector lens E,, which latter throws ad-image of the arsenic image on the halving prism T-l into the left eyepiece. The other moiety of light for the right eye passes through a horizontal rectilinear gap in the left prism 37,, (see Fig. 7 and is reflected on the right hand prism p into the right erector lens E which projects the images into the right eyepiece. The images formed upon the halving prism H are limited or outlined by the circular aperture of the latter.

Now I attain the object of my invention by introducing between the halving lens H and the prism 79,, a separated pair of positive and negative cylindrical achromatic lenses P and N whose vertical cross sections are parallelograms act ng in the vertical plane simply as piecesof parallel glass but curved in horizontal planes so that the pencils of light from the images on the halving prism H, after emergence from the second cylindrical lens N, appear to come from an image at H whose horizontal dimensions are magnified twice or so, while the vertical dimensions are unaffected. Therefore, the circular outlined field is converted into a horizontal oval and an image of this oval image is projected by E and E into the two eyepieces. 4

Fig. 5 shows diagrammatically the action of the two cylindrical lenses in the horizontal or refracting plane. A and B are two points in the principal image, as formed on the halving prism H. P is the positive cylindrical lens of principal focal length i,

the distance H-P being fZ. Therefore, projects an image, ab of A-B, of equal size and at an equal conjugate focal distance behind it. At N, at a distance from c-b equal to one-third of the whole distance Aa, is placed the negative cylindrical lens N of a principal focal length g, which projects a virtual image of a-Z at the points a, and b the two conjugate focal distances being 1 and 2%- so that the final virtual image is magnified twice. Thus, the distance between P and N is correctly two-thirds of the principal focal length of This is a very convenient arrangement because it enables one to command the degree of magnification by simply moving l to and fro without appreciably moving N. For at equal conjugate focal distances, P and P a, if H P is increased by two per cent, P a. is reduced by two per cent. or an almost exactly equal amount, so that image ab remains in about the same position but decreases in size by four per cent. There fore, (l -o and the degree of magn. .ication decreases by four per cent.

T make the two cylindrical achromatic lenses T and I? to the following specification. The double convex lens of P and the double concave lens of N are made of densest barium crown glass having a refractive index for the I) ray of 1.5725 to 1.5735 and a-re-.

ciprocal dispersive power for C to F rays of 57.5. The meniscus flint lens of P and meniscus flint lens of N are made of extra dense flint glass having M :1,647 and a reciprocal dispersive power of.33.9. I The radii of curvatures, taking the surfaces left to right, are Positive Zens P. v

i51 .a thickness: kiegigslhteil gameter=1.000in. T4: 1 Ceuterthxckness=12 1 I Y L N eg'ative lens N. r -4.43 in r== 4.35 inIl l }Flnished diameter =.68 in.

23:}Cnter thickness=J30 Height The plus sign indicates convexity and the minus sign concavity.

The positive lens P should be about 8.25 to 8.5 inches from the image on the halving prism H and the axial distance over the two cylindrical lenses (including their thicknesses) should be about 2.9 inches, for a horizontal magnification of 2.

Figs. Band '7 show the lenses mounted in suitable metal holders, the one carrying the lens N being capable of sliding and carrying it to and fro toward P, and is also capable of being'tilted or rotated about the longitudinal axis by means of the four pushing screws 0. In Fig. 8 the structure appearing in Fig. 6 is shown in elevation, looking'from the left; while Fig. 9 shows the prism 79, as seen from the left, provided with a slot 8 for the passage of a moiety of light toward the prism 10 This is a vitallynecessary adjustment and is performed when throwing a converging cone of rays from an objective 'into the system, the lens N being nearest to the objective, and the image of the point of light to which the cone of rays is converging being examined at a position corresponding to H. If the vertical axes of the lenses P and N are at all out of parallehthe cone of rays, rendered rectangular by the outline of the cylindrical lenses, will not show rectangular sections of the rays when the examining eyepiece is out of focus, but

they will show oblique or rhomboidal'forms,

and the lens N must be rotated by means of the four pushing foot. screws C until the image is quite symmetrical and perfect. The whole frame and lenses are then ready for insertion in the instrument to which they are attachedby three pairs of antagonist screws (1, b. By means of them the. centers of P and N are adjusted into true alinement along the optical axis, with their axes perpendicular to the halving edge at H. ing the lens N to and from P by means of the screw 7, (when the two binding screws OZ are unclamped) will adjust the position of the virtual image at Has formed by the.

rays in horizontal planes, until it lies in the Shiftsame plane as theimage formed by the rays If less, then the distance H to a may be di- U vided more equally by the position of N and they principal focal length of N will then have to be greater. If more, then the position of N will have to divide H to a more unequally and its principal focal length will have to be less accordingly. This is a method alternative to the one before described, wherein the magnification was modified by simply moving Nto and fro alon the axis, P remaining stationary.

What I claim is 1. An optical instrument including means for producing an emergent beam non-circular in form in combination with means J for rendering the beam more circular in form.

2. An optical instrument including means for producing an emergent beam non-circular in form in combination with magnifying means. for rendering the beam more circular in form.

'3. An instrument including means for superimposing two non-circular beams, and

means for render ng said beams-more circular. l l

4. An optical instrumentincluding means for producing a non-circular emergent beam, and a cylindrical lens system for rendering the beam more circular.

'5. An instrument including means for superimposing .two non-circular beams, and

, a cylindrical lens system for rendering the beamv more circular.

6. An optlcal mstrumentmcludmg means for produclng' a non-circular emergent beam,

and a cylindrical lens system adjustable in relation to said first-mentioned means for rendering the beam more circular.

7. An instrument including means for superimposin two non-circular beams and a cylindrical ens system adjustable in rela-. tion to said first-mentioned means for rendering the beaminore circulan' 8. An instrument including. in combination means for superimposing two non-cir cular beams, a cylindrical lens system for rendering the beams more circular, and

means for adjusting at least one lens of said system relatively to another lens. of the system. y Y.

9. An instrument including means for superimposin two non-circular beams and my hand in presence of two subscribing a cyhndrlcal ens system for renderlng the Witnesses.

beams more circular, in combination with HAROLD DENNIS TAYLOR. means for sliding and rotating at least one Witnesses: 5 lens of said system. GEORGE WILLIAM CURRY,

I In testimony whereof I have hereunto set JOHN WILLIAM "HOBSON. 

